For a long time, twin-chamber syringes have been used where a pyrogen-free, sterile solvent is present in one chamber, and a charge, obtained by lyophilizing in the syringe itself, which is dissolved by the pyrogen-free water when the syringe is operated, and then infected, in the second chamber facing the needle.
There is, however, a number of active substances based on human plasma proteins which are activity-sensitive. That means they cannot be kept in solution at higher concentration and over reasonable periods of time, f.i. some hours, because the substance then looses biological activity or can even be degraded and precipitate in part. This is especially true for factor VIII. Preparations of this kind can only be used in a relatively low concentration at present. The concentration in ampoules sized as to be still acceptable for solutions to be injected is too low for injection solutions with a sufficient therapeutic efficiency. Therefore, they are used as infusion solutions. Because these necessarily have to be highly-diluted solutions , the infusion, and therefore the application of the active substance takes a long time. In most cases, however, a rapid application is desired to obtain an effect as fast as possible. However, even for moderately high concentrations of such active substances, the time required for an infusion is often too long as to prevent degradation or deterioration of the substance.
Up to now, for use in direct lyophilization in the twin-chamber syringe, the concentrations which could be obtained in solutions were too low as to obtain a sufficient quantity of the substance in the chamber by a single lyophilization step. For the same reasons which apply to the use of more concentrated solutions, repeated filling and lyophilization in the chamber, however, is not possible because, due to the activity-sensitivity of such human proteins, the protein would be damaged when the chamber is refilled.